Exemplary embodiments of the invention relates to a method for processing wet olive pomace and to a plant for processing wet olive pomace.
German patent document DE 4206006C1 of 16 Sep. 1993 (Düppjohann/Geissen) describes a method in which ground olives are separated in the form of a pulp without the addition of water into the “oil” phase and practically “oil-free pulps”. These pulps, which are made up of the two ingredients fruit water (Spanish Alpechin) as well as oil- and water-free pomaces with about 50% moisture (Spanish Orujo), are termed “liquid pomace” or “wet olive pomace”.
European patent document EP 1 260 571 A1 discloses a method for extracting oil from fruits or seeds, preferably olives or avocados, with a solid bowl screw-type centrifuge and a plant for the oil extraction. The fruits or seeds are thereby pulverized and during or after pulverization are exposed to high pressure and a subsequent slackening, whereupon the pulverized fruit pulp is supplied to the solid bowl screw-type centrifuge. This separates the incoming pulp into oil and pomace (water/solids mixture) or wet olive pomace (“Alpeorujo”).
European patent document EP 0 557 758 A1 discloses a method for extracting olive oil in which a fruit pulp is produced by means of a mill and broken-up in a mixer and then supplied to a solid bowl screw-type centrifuge for the purpose of separating the oil from the fruit pulp. When using fresh olives the production of the fruit pulp can hereby take place without the addition of water, and when using dried olives is carried out with the addition of a slight amount of water according to the state of the olives. The broken-up fruit pulp is separated in a so-called two-phase method more particularly in a two-phase solid bowl screw-type centrifuge into oil and into a solids-water mixture, called “wet olive pomace”. The solids-water mixture is suitable for a subsequent extraction and drying process. This procedure is, however, not always desired. This therefore calls for an advantageous further processing of the wet olive pomace.
Further prior art includes European patent document EP 0 718 397 A1; and PCT patent documents WO2007/042742 A1 and WO 2007/118920 A1.
Exemplary embodiments of the present invention are directed to solving this problem. An advantageous method for processing the wet olive pomace is thus to be provided which can be carried out following the or a two-phase method for the oil extraction.
A method according to the invention for processing wet olive pomace comprises at least the following steps: a) providing wet olive pomace; b) adding a calcium compound and/or a calcium solution to the wet olive pomace; and c) filtering the wet olive pomace in a first separating device to obtain a solid phase and a liquid phase.
By adding calcium in the form of the calcium compound more compact solid particles are formed in the wet olive pomace. At the same time, as a result of the more compact structure of the solid particles, less liquid is bonded by the proportion of solids in the wet olive pomace or retained in the wet olive pomace. This released liquid can be mechanically separated so that a processing of the wet olive pomace is also possible with a view to the end waste disposal and to an economical process management. Through the mechanical separation of the liquid phase from the wet olive pomace the residual moisture content in the liquid-reduced solid phase can be lowered to 50% or less.
The effects of adding a calcium compound lie in a more extensive separation of the liquid or liquor. The solid can be dumped directly as waste. After a phase separation and, where applicable, a further processing even further valuable products (more particularly polyphenols and/or an oil phase) can be obtained from the liquor.
Calcium oxide or lime (foodstuffs additive E529) can advantageously be added to the wet olive pomace as calcium source or compound, or slaked lime (foodstuffs additive E526) can be added as calcium hydroxide and/or wollastonite can be added as calcium (salt solution). Through the shift in the alkali pH value through the addition of these limes, bases or salt solutions or mixtures thereof, polyphenols are also advantageously shifted from the wet olive pomace into the separated liquid phase. These can then be easily isolated from the liquid phase through additional method steps. This optimum extraction of polyphenols makes the method even more economical.
It is moreover advantageous if after preparing the wet olive pomace, according to step a), and preferably prior to adding the calcium compound and/or the calcium solution, according to step b), a mechanical separation of the stones from at least a partial amount of the total amount or from the total amount of wet olive pomace is carried out following an olive oil extraction. These stones can then be dumped or can be used by way of example as fuel (see also FIG. 3). A substantially stone-free wet olive pomace mass of this kind thereby typically has a moisture content of 70-75%, in relation to the total mass of wet olive pomace, and a partially stone-free wet olive pomace mass has a moisture content of 65-70%.
Up until now a mechanical dewatering in the case of such wet sludge could only be carried out up to a residual moisture content of the solid phase of 60-64%. With the method according to the invention it is however possible to carry out a dewatering in a mechanical way wherein the solid phase that is hereby obtained has a residual moisture content of 50%±5%. This remaining solid phase can be dumped as waste, for example.
The amount of added lime to the wet olive pomace should advantageously amount to a maximum of 5%, preferably 2-3%, in relation to the total weight of wet olive pomace, lime or calcium oxide. With a higher addition of lime, liquid is bonded by the lime and cannot be removed from the wet olive pomace through mechanical separation. In order to remove the greatest possible amount of liquid from the wet olive pomace, the proportionate addition of lime of 2-3% has proved particularly expedient.
Starting from the amount of lime added, slaked lime, thus calcium hydroxide, and/or lime water can also be added to the wet olive pomace in a quantity such that it corresponds to the quantity of added lime.
The mechanical separation of a liquid phase from the wet olive pomace by forming a liquid-reduced solid phase can be carried out by a separating device, more particularly in a press.
The processing is preferably carried out before initiating an appreciable fermentation of the product.
A screw press is particularly suitable as a press.
Alternatively a belt press can also be used by way of example as a press.
Alternatively separation can be carried out with a decanter or a filter device.
As a whole the use of a decanter or press has proved particularly advantageous since the proportion of colloidal solids in the separated liquid phase after step c) was comparatively low.
The addition of the calcium oxide and/or the calcium solution can advantageously take place through a dosing unit, preferably as a powder-in-pulp dosing or through the use of a powder dosing machine. The heat that develops during the addition as a result of the exothermic chemical reaction can be controlled by the amount of lime in the dosing unit. A dosing unit furthermore enables a material-saving addition of the corresponding calcium oxide.
The process control can advantageously be carried out by determining and balancing the temperature change in the individual method stages.
A particularly high proportion of liquid phase after the mechanical separation according to step c) could be ascertained when processing fresh wet olive pomace. It is therefore advantageous if the processing of the wet olive pomace from its preparation, according to step a), up to the mechanical separation of the liquid phase from the wet olive pomace by forming the liquid-reduced solid phase, according to step c), is carried out within a maximum of 1 hour, preferably within 30 minutes.
Furthermore a reduction of the residual moisture content could be achieved in the liquid-reduced solid phase by using the wet olive pomace from olives having a degree of ripeness of 4-5, starting from a scale of 1-7, wherein the degree of ripeness 7 indicates the over-ripeness of an olive.
In the case of wet olive pomace obtained from olives with a degree of ripeness of 6-7 or having a standing time before the mechanical separation of the liquid phase, according to step c), of more than 5 h, adding pectin prior to the mechanical separation of the liquid phase, according to step c), has proved expedient in order to separate solids sufficiently from the wet olive pomace.
The liquid phase arising in step c) can be further processed in a further separating device by forming a solid phase, an aqueous phase and where applicable an oil phase. The extraction of polyphenols from the aqueous phase by concentrating the aqueous phase and/or by adsorption has proved particularly advantageous. An additional valuable material can thereby be obtained from a material mixture that hitherto was always rejected as undesired waste. The aqueous phase can be disposed of using a filtration unit.
The residues of the solid phase accumulating during the processing of the liquid phase with a three-phase separation according to step d), can also be recycled in the process. This solid phase need therefore not be stored separately.
According to the invention a plant for processing wet olive pomace comprises at least one mixing device, one dosing unit for the dosed addition of a calcium compound and/or a calcium solution, which opens into the mixing device, and a separating device into which the supply of the wet olive pomace is undertaken from the mixing device and which enables a mechanical separation of a liquid phase by forming a liquid-reduced solid phase.
The dosing unit allows a precise and controlled addition of calcium compound or solution to the wet olive pomace and a uniform distribution of the compound or solution in the wet olive pomace.